The present invention relates to an electric power steering system for a motor vehicle, and more particularly to a system for controlling a motor in accordance with the turning of a steering wheel.
The electric power steering system has a torsion torque sensor for measuring torsion torque in a steering shaft. The system is adapted to control the rotational direction and torque of a motor in dependency on the output signal of the sensor. In order to significantly reduce the driver's steering effort, if the power of the motor is increased, the rotational inertia of the motor increases. The result is that after a turn returnability of the steering-wheel is reduces. In addition, when the vehicle negotiates a corner having a small radius, the steering wheel effort is reduced to a very small value, since the torque of the motor is not changed in accordance with the steering operation speed. Such a light steering load causes uneasiness in the driver.